Ion producing mechanism



Sept. 16, 1958 E. o. LAWRENCE ION PRODUCING MECHANISM 3 Sheets-Sheet 2 Filed NOV. 28, 1945 iiwm ggf/a FIELEL INVENTOR. fave-s7- 0. LAWRENCE BY ATTORNEY.

Se t. 16, 1958 E. o. LAWRENCE 2,852,689

ION PRODUCING MECHANISM Filed Nov. 28, 1945 5 Sheets-Sheet 5 INYENTOR. ERNEST 0. LAWEENCE ATTORNEY.

United States Patent ION PRODUING MECHANISM Ernest 0. Lawrence, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application November 28, 1945, Serial No. 631,417

7 Claims. (Cl. 25041.9)

The present invention relates to the art of treating a polyisotopic substance to produce a plurality of segregable masses wherein the distribution of the constituent isotopes has been altered so that one of the masses produced is enriched with respect to at least one isotope. The purpose of such treatment is to obtain a product characterized by an enhancement of the percentage of a selected isotope. More specifically, the invention relates to the device known in the art as a calutron, a term which has been defined in United States Patent No. 2,709,222 issued May 24, 1955, to Ernest 0. Lawrence, as any apparatus or machine wherein isotope separation or enrichment is achieved on a large scale yielding commercially useful quantities of one or more isotopes, by appropriate separative action on gaseous ions with electrostatic or electromagnetic means or combinations of them.

A source for a calutron includes a chamber for holding a quantity of material capable of being vaporized, a heater for the chamber, a cathode and anode for establishing a stream of electrons, and accelerating electrodes; the whole being so arranged that when the circuits are closed, the material vaporizes and is drawn through the electron stream where ionization takes place. The ions are then drawn through a slit by the accelerating electrodes to form a beam.

The most important object of the invention is to produce an ion beam more efiiciently than has heretofore been accomplished.

Another object of the invention is to provide an ion beam-producing mechanism which is of simple, rugged contruction, and capable of continued operation without undue wear.

Another object of the invention is to provide a calutron ion source having an improved electrode mounting arrangement productive of a uniform and copious supply of ions.

An important feature of the invention resides in a plurality of insulators so mounted as to be accessible from the exterior of the calutron tank and supporting at their inner ends the mechanism by means of which a change of polyisotopic material is vaporized and ionized.

Another feature of the invention consists in arranging the aforesaid insulators in mutually parallel relation and also parallel to the flux in the magnetic field, whereby the strain on the supporting elements is reduced to a minimum.

These and other objects and features of the invention will more easily be understood and appreciated from the following detailed description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings, in which:

Figure 1 is a diagrammatic plan view of a representative calutron in which there may be incorporated an ion source embodying the present invention;

Fig. 2 is a diagrammatic sectional view of the calutron taken along the line 22 of Fig. l;

Patented Sept. 16, 1958 Fig. 3 is a view in side elevation, partlyv in crosssection, of a calutron transmitter constructed in accordance with the invention; and

Fig. 4 is a plan View of the transmitter shown in Fig. 3.

Referring now more particularly to Figs. 1 and 2 of the drawings, there is illustrated a representative example of a calutron 200 of the character noted, that comprises magnetic field structure including upper and lower pole pieces 211 and 212, provided with substan tially flat parallel spaced-apart pole faces, and a tank 213 disposed between the pole faces of the pole pieces 211 and 212. The pole pieces 211 and 212 carrywindings, not shown, which are adapted to be energized in order to produce a substantially uniform and relatively strong magnetic field therebetween, which magnetic-field passes through the tank 213 and the various parts housed therein. The tank 213 is of tubular configuration, being substantially crescent-shaped in plan, and comprising substantially flat parallel spaced-apart top and bottom walls 214 and 215, upstanding curved inner and outer side walls 216 and 217, and end walls 218 and 219. The end walls 218 and 219 close the opposite ends of the tubular tank 213 and are adapted to be removably secured in place, whereby the tank 213 is hermetically sealed. Also, vacuum pumping apparatus, not shown,

is associated with the tank 213, whereby the interior of the tank 213 may be evacuated to apressure of the order of 10- to 10- mm. Hg. Preferably, the component parts of the tank 213 are formed of steel, the topand bottom walls 214 and 216 thereof being spaced a short distance from the pole faces of the upper and lower pole pieces 211 and 212 respectively, the tank 213 being retained in such position in any suitable manner, whereby the top and bottom walls 214 and 215 constitute in ef fect pole pieces with respect to the interior of the tank 213, as explained more fully hereinafter.

The removable end wall 218 suitably supports a source unit 220 comprising a charge receptacle 221 and a communicating arc block 222. An electric heater 223 is arranged in heat exchange relation with the charge toceptacle 221 and is adapted to be connected to a suitable source of heater supply, whereby the charge receptacle 221 may be appropriately heated, the charge receptacle 221 being formed of copper or the like. The are block 222 is formed of copper and is substantially C-shaped in plan, an upstanding slot 224 being formed in the wall thereof remote from the charge receptacle 221. Thus, the arc block 222 is of hollow construction, the cavity therein communicating with the interior of the charge receptacle 221. p

Also, the removable end wall 218 carries a filamentary cathode 225 adapted to be connected to a suitable source of filament voltage supply, the filamentary cathode 225 overhanging the upper end of the arc block 222 and being arranged in alignment with respect to the upper end of the cavity formed therein. Further, the removable end wall 218 carries an anode 226 disposed below the lower end of the arc block 222 and arranged in alignment with respect to the lower end of the cavity formed therein. The tank 213 is grounded. The filamentary cathode 225 and the cooperating anode 226 are adapted to be connected to a suitable source of arc voltage supply.

Further, the removable end wall 218 carries ion accelerating structure 227 formed in part of carbon or graphite, and disposed in spaced-apart relation with respect to the wall of the arc block 222 in which the slot 224 is formed. More specifically a slit 228 is formed in the ion accelerating structure 227 and arranged in substantial alignment with respect to the slot 224 formed in the wall of the arc block 222. A suitable source of accelerating electrode voltage supply is adapted to vbe connected between the arc block 222 and the ion accelerating structure 227,

the positive and negative terminals of the supply mentioned being respectively connected to the arc block 222 and to the ion accelerating structure 227. Further, the negative terminal of the ion accelerating potential is grounded.

The removable end wall 219 suitably supports a collector block 229 formed of stainless steel or the like and provided with two laterally spaced-apart cavities or pockets 230 and 231 which respectively communicate with aligned slots 232 and 233 formed in the wall of the collector block 229 disposed remote from the removable end wall 219.

It will be observed from an inspection of the schematic circuit diagram in Fig. 1 that the negative terminal of the filament supply is tied to the negative side of the arc supply which is bridge by a potentiometer 2, the center tap of which is connected to the arc block and to the positive side of the supply for the accelerating electrodes. The accelerating electrodes and the negative side of the supply thereto are at ground potential. Consequently, the arc block may conveniently be maintained slightly less positive than the anode or at the same potential as the anode. The filament voltage may be of the order of 4 volts, and the arc voltage may be of the order of 100 volts; the accelerating voltage is considerably higher and may be of the order of thirty kilovolts. The voltages are not critical and the values above given are merely illustrative of one combination which has been successfully operated.

Considering now the general principle of operation of the calutron 200, a charge comprising a compound of the element to be treated is placed in the charge receptacle 221, and the various electrical connections are completed and operation of the vacuum pumping apparatus, not shown, associated with the tank 213 is initiated. When a pressure of the order of 10- to mm. Hg is established within the tank 213, the electric circuits for the windings, not shown, associated with the pole pieces 211 and 212 are closed and adjusted, whereby a predetermined magnetic field is established therebetween traversing the tank 213. The electric circuit for the heater 223 is closed, whereby the charge in the charge receptacle 221 is heated and vaporized. The vapor fills the charge receptacle 221 and is conducted into the communicating cavity formed in the are block 222. The electric circuit for the filamentary cathode 225 is closed, whereby the filamentary cathode is heated and rendered electron emissive. Then the electric circuit between the filamentary cathode 225 and the anode 226 is closed, whereby an arc discharge is struck therebetween, electrons proceeding from the filamentary cathode 225 to the anode 226. The electrons proceeding from the filamentary cathode 225 break up the molecular form of the compound of the vapor to a considerable extent, producing positive ions of the element that is to be enriched with the selected one of its isotopes.

The electric circuit between the arc block 222 and the ion accelerating structure 227 is completed, the ion accelerating structure 227 being at a high negative potential with respect to the arc block 222, whereby the positive ions in the arc block 222 are attracted by the ion accelerating structure 227 and accelerated through the voltage impressed therebetween; More particularly, the positive ions proceed from the cavity formed in the arc block 222 through theslot 224 formed in the wall thereof, and across the space between the ion accelerating structure 227 and the adjacent wall of the arc block 222, and thence throughthe slit 228 formed in the ion accelerating structure 227 into the interior of the tank 213. The highvelocity positive ions forms a vertical upstanding ribbon or beam proceeding from the cavity formed in the arc block 222 through the slot 224 and the aligned slit 228 into the tank 213. i

The collector block 229 and the tank are grounded, the same being true of the ion accelerating structure 227,

4 whereby there is an electricfield-free path for the high-' velocity positive ions disposed between the ion accelerating structure 227 and the collector block 229 within the tank 213. The high-velocity positive ions entering the adjacent end of the tank 213 are deflected from their normal straight-line path and from a vetrical plane passing through the slot 224 and the aligned slot 223, due

to the effect of the relatively strong magnetic field mainare set in the flange 20 to improve the seal.

tained through the space within the tank 213 through which the positive ions travel, whereby the positive ions describe arcs, the radii of which are proportional to the square roots of the masses of the ions and consequently of the isotopes of the element mentioned. Thus, ions of a relatively light isotope of the element describe an interior arc of relatively short radius and are focused through the slot 232 into the pocket 230 formed in the collector block 229; whereas ions of a relatively heavy isotope of the element describe an exterior arc of relatively long radius and are focused through the slot 233 into the pocket 231 formed in the collector block 229.

After all of the charge in the charge receptacle 221 has been vaporized, all of the electric circuits are interrupted and the end wall 218 is removed so that another charge may be placed in the charge receptacle 221 and subsequently vaporized in the manner explained above. After a suitable number of charges have been vaporized in order to obtain appropriate deposits of the isotopes of the element in the pockets 230 and 231 of the collector block" 229, the end wall 219 may be removed and the deposits of the collected isotopes in the pockets 230 and 231 in the collector block 229 may be reclaimed.

The present invention relates particularly to the structure employed to support the ion-producing mechanism at the transmitter end of a calutron. As will be evident from an inspection of Fig. 3, there is provided a magnet having an upper pole piece 19 and a lower pole piece 12 between which is inserted a flat tank or vessel having a top wall 14 and a bottom wall 16. The top and bottom walls are held in spaced relation from the pole pieces of the magnet by means of appropriately dimensioned spacer blocks 18.

One portion of the calutron tank is sealed by a removable door or fan plate comprising a peripheral flange 20 held against the edges of the top and bottom walls 14 and 16 by means of C-clamps 22, there being a suflicient num ber of C-clamps to form a pressure tight seal between the flange 20 and the tank walls. A pair of rubber gaskets 24 Welded to the top of the flange 24) is a flat outwardly extending plate or web 26 to the outer end of which is welded a vertical plate 28. A flat plate 30 is welded to the bottom of the flange 20 and is in turn welded to a vertical plate 32 oifset inwardly from the flange 20. Joining the-bottom of the plate 28 and the top of the plate 32 is a horizontal mounting plate 34, welded in place and forming with the walls 30 and 32 a re-entrant chamber or portion of the calutron vessel or tank. The bottom and inner wall of the charm ber thus formed is lined with a layer 36 of insulating material such as asbestos or other suitable heat insulating substance.

The mounting plate 34 is provided with a pair of circular holes 38 through which extend a pair of insulators or insulating bushings 40. Inasmuch as the insulators 40 and their mounts are precisely identical it will be suficient to describe in detail only the one which appears in Fig. 3. It will be seen that the insulator 40, which is made of glass or suitable refractory insulating material, is tubular and is provided with a centrally located annular flange 42. A pair of annular gaskets 44 are contained in recesses cut into the lower surface of the plate 34 and surrounding the aperture 38. The flange 42 of the insulator 40 bears against the gaskets 44. A metal ring 46 surrounds the insulator 40 below the flange 42 and is urged upwardly by means of a series of bolts 48 received in holes tapped in the plate 34. A rubber ring asket 50 is interposed be tween the ring 46 and the flange 42. When the bolts 48 are tightened, the ring 46 clamps the flange 42 tightly against the lower surface of the plate 34, thus serving to mount the insulator 40 in fixed position. It should be stated that the insulators 40 are mutually parallel and their axes are in turn parallel to the direction of the fiux traversing the space between the pole pieces and 12 and indicated in Fig. 3 by the arrow 104. Within each insulator 40 there is a hollow metal tube 52 to the upper end of which is welded a pair of internally projecting metal ears 54 into which holes are tapped for the reception of a series of bolts 56. Over the top of the insulator 40 there is placed an annular rubber gasket 58 upon which bears a cast metal bracket 60 secured in place by means of the bolts 56 and having an outwardly extending portion which serves to support an arc block, as will later be described in detail. The bottom of each tube 52 is welded to an annular plate 66 which is provided with a pair of concentric annular recesses containing a pair of rubber ring gaskets 68 bearing against the lower end of the insulator 40. A metal ring 64 surrounds the lower end of the insulator 40 and is cemented thereto. A series of bolt 70 work against the annulus 66 and are received in holes tapped in the ring 64. Inasmuch as the bolts 56 work against the bracket 60 and tend to force the tube 52 upwardly it will be evident that the bracket 69 ,and the annulus 66 are tightly clamped against opposite ends of the insulator 40, thus compressing the gaskets 58 and 68 to form an etfective vacuum seal.

The annulus 66 is sectionally apertured to receive a plug 72 containing four vacuum seal sleeves 76 through which pass two stiif water-cooled electric leads 74 and two similar leads 74'. As shown in Fig. 3 the lead 74' extend through the interior of the insulator 40 and through an opening 75 in the bracket 60 where they are received in a pair of blocks 78. The blocks serve as right-angle joints between the vertical portion of the leads 74 and horizontally extending portions which run across the top of the bracket 6%) parallel to the upper surface thereof.

The bracket 69 has a peripheral depending skirt or flange 62 and terminates at its inner end in a vertical wall 80 to which is secured a metal block 82 provided with an interior chamber 86 connected to the reservoir 84 for charge material by means of a conduit 85. As shown in Fig. 4, the block 82 is also provided with three elongated narrow vertical chambers 88 which communicate with the chamber 86. Each of the chambers 88 is provided with an exit slit 89 in advance of which is disclosed a slotted accelerating electrode 1130 supported from the bottom wall 16 of the calutron tank by means of a bracket 102.

Upon inspection of Fig. 4 it will be seen that through one of these insulators 40 two pairs of water-cooled leads 74 and 74' extend to overlie two of the chambers 88 and on a complete pair of leads there is supported a filamentary cathode 90. From the other insulator there extends a pair of cathode leads 74 which serve a third filament 99. Through the same insulator there also extends a pair of metal tubes 108 which extend across the top of the bracket 64) and are wrapped about the block 82. The tubes 108 serve two functions. In order to operate the calutron a high positive voltage must be applied to the casting S2 and this voltage is impressed upon the tubes 1%. Furthermore, a fluid-coolant is circulated through the tubes 1% and to cool the block 82 and prevent overheating thereof. The accelerating electrodes 10 maintain the same potential as the walls 14 and 16 of the tank.

The operation of the calutron shown in Figs. 3 and 4 is the same as in the representative apparatus discussed in connection with Figs. 1 and 2. However, the mounting of the main supporting elements, the insulators 40, parallel to the direction of the flux results in an important reduction in destructive stresses operating on the equipment. Moreover, the provision of the re-entrant chambers in combination with the transverse mounting wall 34 ofiers considerable improvement over prior devices in particular connection with the assembly and adjustment of the elements. It is easily possible to assemble the elements quickly and securely, both ends of the insulators being readily accessible.

Having now described and illustrated a preferred embodiment of my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a calutron having an evacuated vessel adapted for traversal by a magnetic field, means removably securing ion-producing mechanism within said vessel including, a removable wall portion of the vessel, an elongated insulating bushing mounted in said removable wall portion and having its long axis substantially parallel to the direction of said magnetic field flux, the inner end of said bushing being disposed within said vessel in spaced relation to said wall portion, ion-producing mechanism disposed within said vessel and spaced from the walls thereof, and means supporting said mechanism upon the inner end of said bushing.

2. In a calutron having an evacuated vessel adapted for traversal by a magnetic field, means removably securing ion-producing mechanism within said vessel including, a removable wall portion of the vessel, an elongated insulating bushing mounted in said removable wall portion and having its long axis substantially parallel to the direction of said magnetic field flux, the inner end of said bushing being disposed within said vessel in spaced relation to said wall portion, ion-producing mechanism disposed within said vessel and spaced from the walls thereof, and cantilever means supporting said mechanism upon the inner end of said bushing.

3. In a calutron having an evacuated vessel adapted for traversal by a magnetic field, means removably securing ion-producing mechanism within said vessel including a removable wall portion of the vessel, said portion comprising an outer wall section, an inwardly olfset wall section and a plate connecting said sections, an elongated insulating bushing mounted in said plate and having its long axis substantially parallel to the direction of said magnetic field flux, the inner end of said bushing being disposed within said vessel in spaced relation to said plate, ion-producing mechanism disposed within said vessel and spaced from the walls thereof, and means supporting said mechanism upon the inner end of said bushing.

4. In a calutron having an evacuated vessel adapted for traversal by a magnetic field, means removably securing ion-producing mechanism within said vessel including, a removable wall portion of the vessel, said portion comprising an outer wall section, an inwardly ofiset wall section and a plate connecting said sections, a plurality of elongated insulating bushings mounted in said plate and having their long axes substantially parallel to the direction of said magnetic field flux, the inner ends of said bushings being disposed within said vessel in spaced relation to said plate, ion-producing mechanism disposed within said vessel and spaced from the walls thereof, and means supporting said mechanism upon the inner ends of said bushings.

5. In a calutron having an evacuated vessel adapted for traversal by a magnetic field, means removably securing ion-producing mechanism within said vessel including, a removable wall portion of the vessel, said portion comprising an outer wall section, an inwardly offset wall section and a plate connecting said sections, a plurality of elongated insulated bushings mounted in said plate and having their long axes substantially parallel to the direction of said magnetic field flux, the inner ends of said bushings being disposed within said vessel in spaced relation to said plate, ion-producing mechanism disposed within said vessel and spaced from the walls thereof, electrical conductors extending through said bushings from the exterior of said vessel and connected to said mechanism, means sealing said conductors within said bushings,

, 7 t and means supporting said mechanism upon the inner ends of said bushings.

6. Apparatus as described in claim 5 wherein said electrical conductors comprise hollow tubular members.

7. Apparatus as described in claim 5 wherein said electrical conductors comprise hollow tubular members having a cooling medium therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,143,327 Snook et a1. June 15, 1915 1,180,998 1 Gibson Apr. 25, 1916 1,894,593 Lamm Jan. 17, 1933 8 Gaston Oct. 31, 1933' Lamm Dec. 17, 1935 Vasselli Feb. 23, 1937 Bahls Feb. 14, 1939 Vienneau Feb. 29, 1944 Langmuir Mar. 6, 1945 Beggs Nov. 19, 1946 OTHER REFERENCES 10 Coggeshall and Jordan: Review Scientific Instruments,

May 194-3, vol. 14, pp. 125-127.

Newhall: Physical Review, July 1 and 15, vol. 62, pp. 

